Tuberculosis (TB) is an airborne bacterial infection caused by the organism Mycobacterium tuberculosis that primarily affects the lungs, although other organs and tissues may be involved.

Key Points

  • While contagious, TB is not easily spread from person to person.
  • About 1.8 billion people, or one-quarter of the world's population, are infected with tuberculosis but most of these people have latent TB.
  • About 10 million people have active TB worldwide.
  • In the United States, TB is much less common.TB can almost always be treated and cured if you take medicine as directed.

How TB Affects Your Body

TB is caused by the bacterium M. tuberculosis. It spreads person to person when an infected individual coughs or sneezes out the bacteria, spreading it through the air to be breathed in by others. It takes prolonged exposure to become infected with TB, so you would typically get sick from a close family member or co-worker, not a casual acquaintance. Once you have inhaled the bacterium, the bacterium lodges in the lung tissue.

Healthy individuals may contract latent TB, but the disease may not become active until months or years later, at a time when the immune system becomes weak for some reason. However, people with weakened immune systems are at a greater risk for developing active TB right away. When they breathe in the bacterium, it settles in their lungs and starts growing because their immune systems cannot fight the infection. In these instances, TB disease may develop within days or weeks after the infection.

When a person gets active TB disease, it means TB bacteria are multiplying and attacking the lung(s) or other parts of the body, such as the lymph nodes, bones, kidney, brain, spine and even the skin. From the lungs, TB bacteria move through the blood or lymphatic system to different parts of the body.

Who Is at Risk of TB?

The chances of getting infected by the TB germ are highest for people that are in close contact with others who are infected. This includes:

  • Family and friends of a person who is infected
  • People from parts of the world with high TB rates, including India and parts of Asia and Africa. 
  • People in groups with high rates of TB transmission, including the homeless, injection drug users and people living with HIV
  • People who work or reside in facilities that house high risk people such as hospitals, homeless shelters, correctional facilities, nursing homes and residential homes for those with HIV

Not everyone who is infected with the TB germ (latent TB) develops clinically active TB disease. People at the highest risk for developing active TB disease are those with a weak immune system, including:

  • Babies and young children
  • People with chronic conditions such as diabetes or kidney disease
  • People with HIV/AIDS
  • Organ transplant recipients
  • Cancer patients undergoing chemotherapy
  • People receiving certain treatments for autoimmune disorders such as rheumatoid arthritis or Crohn's disease

Reviewed and approved by the American Lung Association Scientific and Medical Editorial Review Panel.

Page last updated: June 7, 2024

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